feat(blog): add first/after template functions and listPages config

[corylanou]

Summary

Adds generic template infrastructure inspired by Hugo's template functions:

• first N .Items — returns the first N items from any slice (bounds-safe)
• after N .Items — returns items after the Nth item from any slice (bounds-safe)
• listPages config option — render the list template at additional paths beyond /, each with a .PagePath field so templates can conditionally show different content

These are generic features with no site-specific logic. Templates decide what to render.

Example usage in templates

{{/* Homepage: show latest 3 articles */}}
{{range first 3 .Articles}}...{{end}}

{{/* Check which list page we're on */}}
{{if eq .PagePath "/"}}...{{else}}...{{end}}

Example config

listPages:
  - blog
  - archive

This renders the list template at /blog/index.html and /archive/index.html in addition to /index.html.

Test plan

• go test ./blog/... passes
• first 3 .Articles returns at most 3 items, handles fewer gracefully
• after 2 .Articles skips the first 2 items
• listPages: [blog] generates /blog/index.html with .PagePath set to /blog/
• Homepage .PagePath is /

[chatgpt-codex-connector]

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